gitignore: add explicit list of private files to ignore

.gitignore

@@ -71,4 +71,10 @@
 /jme3-android-native/openal-soft/
 /jme3-android-native/OpenALSoft.zip
 /jme3-android-native/stb_image/
-/jme3-bullet-native-android/build/
+/jme3-bullet-native-android/build/
+/sdk/nbproject/private/private.xml
+/sdk/nbproject/private/platform-private.properties
+/sdk/jme3-scenecomposer/nbproject/private/private.xml
+/sdk/jme3-core/nbproject/private/private.xml
+/.nb-gradle/profiles/private/aux-config
+/build/tmp/mergedJavadoc/javadoc.options